Data Cleaning and Quality Validation in SQL Questions
Handle NULL values, duplicates, and data type issues within queries. Implement data validation checks (row counts, value distributions, date ranges). Practice identifying and documenting data quality issues that impact analysis reliability.
MediumTechnical
0 practiced
Write SQL that profiles a table automatically: for each column compute distinct_count, top_5_values with counts, null_rate, min, max (if numeric/date), and a sample of 5 random values. Assume the table is moderate size and provide an approach that generalizes to many tables programmatically.
HardTechnical
0 practiced
Write a stored procedure or UDF pseudocode in SQL that validates customer lifecycle continuity: for each customer_id, ensure there are no gaps exceeding 90 days between consecutive activity dates. The procedure should output offending customer_ids and the gap details. Provide SQL logic or pseudocode compatible with a modern data warehouse.
MediumTechnical
0 practiced
Write SQL to validate Slowly Changing Dimension (SCD) Type 2 history: ensure for each natural_key there are no overlapping effective_date ranges, each row has non-null effective_from and effective_to (end open to future), and the most recent row has a null effective_to. Provide the queries and describe how to locate offending rows with example output.
HardTechnical
0 practiced
Define a set of KPIs for data quality in a product analytics platform (examples: timely-load-rate, row-reconciliation-failures, schema-drift-rate, critical-null-rate). For each KPI, state how you would calculate it in SQL, acceptable thresholds, and how to operationalize into dashboards, SLAs, and team responsibilities.
HardTechnical
0 practiced
As a senior data scientist, you need to convince data engineering to add source-side constraints (e.g., NOT NULL on critical fields). Draft a concise SQL-backed argument with sample queries that quantify current errors, estimate business impact, and propose an incremental rollout plan to minimize producer disruption.
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